/Engine/Source/Runtime/Engine/Public/SpanAllocator.h
Allocator for spans from some range that is allowed to grow and shrink to accomodate the allocations. Implementation is biased towards the case where allocations and frees are performed in bulk, if they are interleaved performance will degrade. Prefers allocations at the start of the range, such that the high-watermark can be reduced optimally. Primarily optimized for the use-case where span size == 1, for variable span size allocation performance is sub-optimal as it does not accelerate the search for larger allocs.
class FSpanAllocator